Environmental Engineering Reference
In-Depth Information
6. Energy self-sufficiency:
a biorefinery plant should have the aim to run in a sustainable
way: all the energy requirements of the several biomass conversion processes should be
internally supplied by the production of heat and electricity from combustion of residues.
For instance, in a lignocellulosic ethanol plant, lignin, after separation from cellulose and
hemicellulose, can be burnt to provide the heat and electricity required by the plant.
However, direct external fossil energy inputs are allowed if they ensure economic
benefits to the system and do not unduly burden the overall GHG and energy balances.
7. Wasteminimization:
solid, liquid and gaseous wastes released by a biorefinery should be
minimized. This target can be achieved in two ways: using the different biomass
components for producing a wide spectrum of multiple products, or setting up “bio-
clusters”, where material flow exchanges among different plants are promoted in order to
transform a downstream residue of a plant into an upstream raw material for another plant.
2.3. Fossils vs. Biomass as Raw Materials
The structure of biorefinery raw materials is totally different from that on which the
current oil refinery is based. Crude oil is a mixture of many different organic hydrocarbon
compounds (based on C and H) while biomass is made of different compounds (with a large
abundance of O and ashes). The first step of oil refinery is to remove water and impurities,
then distill the crude oil into its various fractions as gasoline, diesel fuel, kerosene, lubricating
oils and asphalts. Then, these fractions can be chemically changed further into various
industrial chemicals and final products.
Unlike petroleum, biomass composition is not homogeneous, because the biomass
feedstocks might be made of grains, wood, grasses, biological wastes and so on, and the
elemental composition is a mixture of C, H and O (plus other minor components such as N, S
and other mineral compounds). This biomass compositional variety is both an advantage and
a disadvantage. An advantage is that biorefineries can make more classes of products that can
petroleum refineries and can rely on a wider range of raw materials. A disadvantage is that a
relatively larger range of processing technologies is needed, and most of these technologies
are still at a pre-commercial stage (Dale and Kim, 2006).
In order to be used for production of biofuels and chemicals, biomass needs to be
depolymerized and deoxygenated. Deoxygenation is required because the presence of O in
biofuels reduces the heat content of molecules and usually gives them high polarity, which
hinders blending with existing fossil fuels (Lange, 2007). Chemical applications may require
much less deoxygenation, since the presence of O often provides valuable physical and
chemical properties to the product.
The main benefits which can be related to an extensive deployment of biorefinery in
replace of oil refinery are based on the supply of renewable biomass. In fact, if this is
managed with sustainable practices, biomass has a closed carbon cycle: its use release to the
atmosphere almost the same amount of CO
2
that was captured during the photosynthetic
process. Furthermore, unlike fossil resources, biomass resources are locally available for
many countries and their provision, together with an implementation and development of
biorefinery industries, will create a large number of jobs, especially in rural areas. Therefore,
biorefinery technologies should be compact and suitable for local installations.
